Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Dec. 31, 2016		Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount primarily related to deferred taxes on appreciation of investment value		$ 333		$ 314
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		105		64
Total assets		2,541		2,321
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Total assets		687		658
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Total assets		181		259
Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Total assets	[1]	(18)		19
Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		105		64
Total assets		3,575		3,428
Nuclear Decommissioning Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		9		36
Global equity securities		1,724		1,520
Fixed-income securities		665		694
Total assets		2,398		2,250	[2]
Assets measured at NAV		0		0
Nuclear Decommissioning Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Global equity securities		0		0
Fixed-income securities		527		521
Total assets		527		521	[2]
Assets measured at NAV		0		0
Nuclear Decommissioning Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Global equity securities		0		0
Fixed-income securities		0		0
Total assets		0		0
Assets measured at NAV		0		0
Nuclear Decommissioning Trusts [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Global equity securities		0		0
Fixed-income securities		0		0
Total assets		0		0
Assets measured at NAV		0		0
Nuclear Decommissioning Trusts [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		9		36
Global equity securities		1,724		1,520
Fixed-income securities		1,192		1,215
Total assets		2,939		2,784	[2]
Assets measured at NAV		14		13
Price Risk Management Instruments [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		30		0
Electric		30		0
Gas		0		0
Electric		9		69
Gas		0		0
Total liabilities		9		69
Price Risk Management Instruments [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		29		10
Electric		18		9
Gas		11		1
Electric		12		1
Gas		2		2
Total liabilities		14		3
Price Risk Management Instruments [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		181		259
Electric		181		259
Gas		0		0
Electric		126		170
Gas		0		0
Total liabilities		126		170
Price Risk Management Instruments [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		(18)		19	[1]
Electric		(18)		18	[1]
Gas		0		1
Electric	[1]	(21)		(70)
Gas		(1)	[1]	(1)
Total liabilities	[1]	(22)		(71)
Price Risk Management Instruments [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		222		288
Electric		211		286
Gas		11		2
Electric		126		170
Gas		1		1
Total liabilities		127		171
Rabbi Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-income securities		0		0
Life insurance contracts		0		0
Total assets		0		0
Rabbi Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-income securities		61		57
Life insurance contracts		70		70
Total assets		131		127
Rabbi Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-income securities		0		0
Life insurance contracts		0		0
Total assets		0		0
Rabbi Trusts [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-income securities		0		0
Life insurance contracts		0		0
Total assets		0		0
Rabbi Trusts [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed-income securities		61		57
Life insurance contracts		70		70
Total assets		131		127
Long-Term Disability Trust [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		8		7
Total assets		8		7
Assets measured at NAV		0		0
Long-Term Disability Trust [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Total assets		0		0
Assets measured at NAV		0		0
Long-Term Disability Trust [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Total assets		0		0
Assets measured at NAV		0		0
Long-Term Disability Trust [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		0		0
Total assets		0		0
Assets measured at NAV		0		0
Long-Term Disability Trust [Member] | Estimate Of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments		8		7
Total assets		178		165
Assets measured at NAV		$ 170		$ 158

[1] Includes the effect of the contractual ability to settle contracts under master netting agreements and margin cash collateral.

[2] Represents amounts before deducting $333 million and $314 million at December 31, 2016 and 2015, respectively, primarily related to deferred taxes on appreciation of investment value.